Rest Post call with Authentication Token

Question

I'm trying to send a Post request to SharePoint Online (Claims Based Auth Site) from my client application (WPF application). In this case it should be an update to a ListItem to change the 'Title' to 'Test'.

I'm retrieving the CookieContainer via MsOnlineClaimsHelper Class which successfully returns me an auth token.

But when i try to send the request the response is The remote server returned an error: (403) Forbidden.

WebRequest Code

try
{
    var claimshelper = new MsOnlineClaimsHelper(baseUrl, _userName, _password);
    var request = (HttpWebRequest)WebRequest.Create(baseUrl + "/" + url);

    request.CookieContainer = claimshelper.CookieContainer;
    request.Method = "POST";
    request.Headers.Add("X-HTTP-Method", "MERGE");
    request.Headers.Add("If-Match", "*");
    request.Accept = "application/json;odata=verbose";

    using (var streamWriter = new StreamWriter(request.GetRequestStream()))
    {
        streamWriter.Write(json);
        streamWriter.Flush();
    }

    var webResp = request.GetResponse() as HttpWebResponse;
    var theData = new StreamReader(webResp.GetResponseStream(), true);
    string payload = theData.ReadToEnd();
}
catch (Exception ex)
{


}

Rest Url:

/_api/lists/getbytitle('SampleList')/items(1)

Json Payload:

string json = "{ '__metadata': { 'type': 'SP.Data.SampleListListItem' }, 'Title': 'Test'}";

Error:

The remote server returned an error: (403) Forbidden.

Answer 1

This error occurs since SharePoint 2013 REST service requires the user to include a Request Digest value with each create, update and delete operation. This value is then used by SharePoint to identify non-genuine requests.

How to provide Request Digest value

In MsOnlineClaimsHelper class (MsOnlineClaimsHelper.cs file) add the following method to request Form Digest value:

/// <summary>
/// Request Form Digest value
/// </summary>
/// <returns></returns>
private string GetFormDigest()
{
    var endpoint = "/_api/contextinfo";
    var request = (HttpWebRequest) WebRequest.Create(_host.AbsoluteUri + endpoint);

    request.CookieContainer = new CookieContainer();
    request.Method = "POST";
    //request.Accept = "application/json;odata=verbose";
    request.ContentLength = 0;

    using (var response = (HttpWebResponse)request.GetResponse())
    {
         using (var reader = new StreamReader(response.GetResponseStream()))
         {
             var result = reader.ReadToEnd();

             // parse the ContextInfo response
             var resultXml = XDocument.Parse(result);

             // get the form digest value
             var e = from e in resultXml.Descendants()
                                 where e.Name == XName.Get("FormDigestValue", "http://schemas.microsoft.com/ado/2007/08/dataservices")
                            select e;
             _formDigest = e.First().Value;   
         }
    }
    return _formDigest;
}

and FormDigest property:

private string _formDigest;
public string FormDigest
{
    get
    {
       if (_formDigest == null || DateTime.Now > _expires)
       {
           return GetFormDigest();
       }
       return _formDigest;
    }
}

How to perform an update operation for a ListItem using SharePoint 2013 REST API

The following example demonstrates how to perform an update of a list item using the provided implementation for requesting a Form Digest

Key Points:

• X-RequestDigest header is used to specify Form Digest value
• Request Content Type have to be specified

Example:

var userName = "username@contoso.onmicrosoft.com";
var password = "password";
var payload = "{ '__metadata': { 'type': 'SP.Data.TasksListItem' }, 'Title': 'New Tasl'}";  //for a Task Item


try
{
    var claimshelper = new MsOnlineClaimsHelper(baseUrl, _userName, _password);
    var request = (HttpWebRequest)WebRequest.Create(baseUrl + "/" + endpointUrl);

    request.CookieContainer = claimshelper.CookieContainer;
    request.Headers.Add("X-RequestDigest", claimshelper.FormDigest);
    request.Method = "POST";
    request.Headers.Add("X-HTTP-Method", "MERGE");
    request.Headers.Add("If-Match", "*");
    request.Accept = "application/json;odata=verbose";
    request.ContentType = "application/json;odata=verbose";

    using (var writer = new StreamWriter(request.GetRequestStream()))
    {
        writer.Write(payload);
        writer.Flush();
    }

    var response = request.GetResponse() as HttpWebResponse;
    //...
 }
 catch (Exception ex)
 {
    //Error handling goes here.. 
 }